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====== Bipolar current driver======
A bipolar current driver that can output up to 8A continouosly if you can cool it. It is based on the opa549 OPamp. The idea comes from the paper "Ultra-low noise and high bandwidth bipolar current driver for precise magnetic field control", https://doi.org/10.1063/1.5046484. Have fun.

Up to now it has only been tested for current up to 1A and in the electronic workshop.

==== Date====
Start of the project: Middle of 2021      /* Die Zeit zu der das Projekt begonnen wurde */             

==== Author ====
Martin Quensen, quensen@iqo.uni-hannover.de    /* Auf wessen Mist das Ding gewachsen ist. Default: Der User, der die Dokuwikiseite anlegt.*/

==== Anwender ====
None, so far. /* Wer das Ding bisher benutzt */

==== Schematic and layout ====
A OPA549 gives out some current that is send through some device (e.g. a coil) and finally a reference resistor. The voltage drop there is measured with an instrumentation amplifier. At an OPamp in PI-controller circuit it is compared to a setpoint signal and the "error signal" is then proportionally amplified and integrated over. The resulted voltage is now applied at the OPA549, that is in non-inverting amplifier configuration. The setpoint signal can be applied via BNC, and there is also the option to use a trimmer for a constant offset.

The OPA549 features a logic signal to shut it down, and a pin for setting a current limit. Both functions are implemented.

The layout is designed as two boards. One for the control (reference resistor, PI OPamp, instr. amps ...) and the other for the OPA549.

It is meant to fit inside a standard 19" 1 HE casing. 

  * {{ :eigenbau:bipolar_current_driver:control_board_schematic_2021-07-10.pdf |Schematic of control board}}
  * {{ :eigenbau:bipolar_current_driver:opa549_board_schematic_2021-07-10.pdf |Schematic of OPA549 board}}
  * {{:eigenbau:bipolar_current_driver:control_board.png?400|Layout of control board as png}}
  * {{:eigenbau:bipolar_current_driver:opa549_board.png?400|Layout of OPA549 board}}
  * Git: [[https://git.iqo.uni-hannover.de/elektroniq/bipolar_opa549_current_driver|Here]]


==== Issue list ====
What to improve: (:no:: discarded, :Ok:: at work, :OK:: done 8-) )
  * There are too many pads for the output current. Not needed.
  * The PI-controller OPamp has a pin distribution that does not fit to its footprint, I think.
  * There is no option to discharge the Elko's in the OPA549 board. They remain charged for quite some time after turning off the power supply.